From d4f863e7a3f1ce3c36acbbe133d515f639d86f62 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Sun, 4 Oct 2026 01:11:40 +0100
Subject: [PATCH] Fix unnormalized tuple in deferred type alias

---
 mypy/semanal.py                         | 12 ++++++++----
 test-data/unit/check-python312.test     | 11 +++++++++++
 test-data/unit/check-typevar-tuple.test | 13 +++++++++++++
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index 5ef5223c2346..251e4115bd66 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -5904,7 +5904,9 @@ def visit_type_alias_stmt(self, s: TypeAliasStmt) -> None:
                 python_3_12_type_alias=True,
             )
             alias_node.default_depends = default_depends
-            s.alias_node = alias_node
+            if s.alias_node is None:
+                # If there is an existing node, it will be modified in-place.
+                s.alias_node = alias_node
 
             updated = False
             if (
@@ -6329,9 +6331,11 @@ def analyze_type_application(self, expr: IndexExpr) -> None:
         if types is None:
             return
         base = expr.base
-        expr.analyzed = TypeApplication(base, types)
-        expr.analyzed.line = expr.line
-        expr.analyzed.column = expr.column
+        if not isinstance(expr.analyzed, TypeAliasExpr):
+            # Do not re-point r.h.s. of a type alias, it is all set.
+            expr.analyzed = TypeApplication(base, types)
+            expr.analyzed.line = expr.line
+            expr.analyzed.column = expr.column
 
         if isinstance(base, RefExpr) and base.fullname == "librt.vecs.vec":
             # Apply restrictions specific to vec
diff --git a/test-data/unit/check-python312.test b/test-data/unit/check-python312.test
index 9d32689a1e98..19b4f1d8b1f1 100644
--- a/test-data/unit/check-python312.test
+++ b/test-data/unit/check-python312.test
@@ -2401,3 +2401,14 @@ reveal_type(baz(objs))  # N: Revealed type is "builtins.list[__main__.B | __main
 reveal_type(baz(objs_a))  # N: Revealed type is "builtins.list[__main__.B | __main__.C]"
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-full.pyi]
+
+[case testDeferredNestedTupleAliasNewSyntax]
+type Inner = tuple[int, str]
+type Outer = tuple[bool, *Inner]
+
+class K(Base):
+    q: list[Outer] = list()
+
+class Base: ...
+reveal_type(K.q)  # N: Revealed type is "builtins.list[tuple[builtins.bool, builtins.int, builtins.str]]"
+[builtins fixtures/tuple.pyi]
diff --git a/test-data/unit/check-typevar-tuple.test b/test-data/unit/check-typevar-tuple.test
index 232d516da85b..37863e6b979f 100644
--- a/test-data/unit/check-typevar-tuple.test
+++ b/test-data/unit/check-typevar-tuple.test
@@ -3232,3 +3232,16 @@ def foo(x, *args):
 def test(f: Callable[[object], object]) -> None: ...
 test(foo)  # E: Argument 1 to "test" has incompatible type overloaded function; expected "Callable[[object], object]"
 [builtins fixtures/tuple.pyi]
+
+[case testDeferredNestedTupleAlias]
+from typing import Unpack
+
+Inner = tuple[int, str]
+Outer = tuple[bool, Unpack[Inner]]
+
+class K(Base):
+    q: list[Outer] = list()
+
+class Base: ...
+reveal_type(K.q)  # N: Revealed type is "builtins.list[tuple[builtins.bool, builtins.int, builtins.str]]"
+[builtins fixtures/tuple.pyi]